This application is made in response to CREG announcement DCCP-18 entitled "Herpesvirus-Induced Malignancy," dated April 1, 1976. The objective of this proposed research is to define the mechanisms by which expression of herpes simplex virus (HSV) genes in transformed cells is regulated, as part of the overall effort to define the mechanism of herpesvirus-induced oncogenesis. Our investigations will focus initially on the regulation of viral thymidine kinase (tk) synthesis in transformed mouse L cell lines (LVtk positive cells) that were derived from Ltk minus cells after their exposure to UV-inactivated HSV and selection for the tk positive phenotype. Our previous studies revealed that the HSV tk gene present in the LVtk positive cells remained subject to regulation by the products of a super-infecting HSV(tk negative) genome and raised the possibility that synthesis of viral tk in the LVtk positive cells might be regulated by the products of other HSV genes introduced during transformation. We intend to investigate this possibility by identifying and characterizing other HSV products that are expressed in two variants of the LVtk positive cells, i.e. cells that synthesize viral tk and those that fail to synthesize the enzyme although they retain the HSV tk gene. The approaches to be taken include the isolation of host-range mutants whose defects can be complemented by HSV products made in LVtk positive cells and the use of specific antibodies for detecting viral proteins. We also intend to identify the regions of the HSV genome that are retained and transcribed in several LVtk positive cell lines. Tools developed for the detection of specific HSV gene products will be used also to investigate HSV gene expression in tumorigenic HSV-transformed hamster cell lines.